Actelion Ltd. (ATLN) is once again shaping up as a takeover candidate after the lung-disease drug on which the company staked its future won regulatory approval. The drugmaker, which has a market value of 8.3 billion Swiss francs ($9.3 billion), was granted U.S. approval on Oct. 18 for Opsumit, a pill to treat pulmonary arterial hypertension that may generate $1.1 billion in annual revenue by 2017, according to analysts’ estimates compiled by Bloomberg.